1. Field of Invention
The method and apparatus of the present invention relates to an improved process to induce under balanced conditions by gas lifting fluids from a vertical or non-vertical well bore while drilling.
2. The Prior Art
An under balanced drilling condition exists when the hydrostatic pressure exerted by fluids in the well bore is less than the pore pressure contained within the reservoir being drilled. This low-pressure environment permits formation fluids such as oil and gas to enter the well bore while drilling. The under balanced state can be achieved by injecting a density reducing agent such as gas into the column of fluid near the bottom of the well where it combines with the fluids, both drilling and production, contained in the well bore causing a reduction in the fluid density. This gasified liquid reduces the density of the fluid which in turn lowers the hydrostatic pressure exerted by the fluid column to a point that can be less than the pressure residing within a formation thereby allowing oil, gas and water to be produced while drilling. Under balanced techniques are usually applied when drilling under pressured reservoirs.
The present invention improves the ability of a gas delivery system commonly known as the concentric casing technique to not only inject gas into the fluid but actually pump and lift fluids from a well by creating a venturi pump and vortex around the drill pipe. The apparatus includes a production casing extending vertically from the ground to the area where the drilling is taking place. A concentric casing is mounted within the production casing to form an outer annulus. The drill string extends downwardly through the concentric casing and terminates with a drill bit, which is located in the area where the drilling is to take place. The drill string connects with an injection tool, which in turn connects with a packer. The packer isolates the outer annular space between the production casing and the concentric casing thereby directing compressed gas to travel down the well to the packer. The injection tool includes a generally cylindrical body with a plurality of flutes or vanes which extend out to the inner circumference of the production casing so as to permit fluid coming down the concentric annulus to go between the flutes and past the injection tool until it reaches the packer. The spiral flutes or vanes of the injection tool are provided with longitudinal passageways, each of which is in the shape of an elongated venturi. When fluid (gas) passes beyond the injection tool and against the packer, it has only one place to go and that is through the spiral venturi passageways in the flutes and into the inner annulus between the concentric casing string and the drill pipe. This space is also referred to as the return annulus because it provides a path for drill cuttings, oil, gas, and water to be recovered from the well. The passageways leading to the nozzles spirals upwards causing a vortex to be generated when the gas enters the inner annulus. This allows the injected gas to more completely mix with the well bore fluids and thus prevent the compressed gas from separating and channeling through the fluids in the return annulus. This injection process, which can be described as an aspiration, also creates a pressure differential in the return annulus as the compressed gas passes through the nozzle orifice. This helps to draw the fluids upwards from the lower part of the well bore thereby assisting in the recovery of well bore fluids during the drilling process.